The present invention relates generally to disk drive systems and, more particularly, to a system and method for extending the service life of a magnetoresistive element of a read/write head.
A typical disk drive system includes a magnetic medium for storing data in magnetic form and a number of transducers used to write and read magnetic data respectively to and from the medium. A typical disk storage device, for example, includes one or more data storage disks coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute (RPM).
Digital information is typically stored in the form of magnetic transitions on a series of concentric, spaced tracks formatted on the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a number of sectors, with each sector comprising a number of information fields, including fields for storing data, and sector identification and synchronization information, for example.
An actuator assembly typically includes a plurality of outwardly extending arms with one or more read/write head assemblies being mounted thereon by use of flexible suspensions. A typical read/write head assembly is understood to include a slider body, a read element, and a write element. The slider body lifts the read/write elements off the surface of the disk as the rate of spindle motor rotation increases, and causes the read/write elements to hover above the disk on an air bearing produced by high speed disk rotation. The distance between a read/write head and the disk surface, which is typically on the order of 40-100 nanometers (nm), is commonly referred to as head-to-disk clearance or spacing.
Writing data to a magnetic data storage disk generally involves passing a current through a write element of the read/write head assembly to produce magnetic lines of flux which magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by a read element of the read/write head assembly sensing the magnetic field or flux lines emanating from the magnetized locations of the disk. As the read element passes over the rotating disk surface, the interaction between the read element and the magnetized locations on the disk surface results in the production of electrical signals, commonly referred to as readback signals, in the read element.
Conventional disk drive systems generally employ a closed-loop servo control system for positioning the read/write elements, or transducers, to specified storage locations on the data storage disk. During normal disk drive system operation, a servo transducer, generally mounted proximate the read/write transducers, or, alternatively, incorporated as the read element of the read/write head assembly, is typically employed to read information for the purpose of following a specified track (i.e., track following) and locating (i.e., seeking) specified track and data sector locations on the disk.
In accordance with one known servo technique, embedded servo pattern information is written to the disk along segments extending in a direction generally outward from the center of the disk. The embedded servo patterns are thus formed between the data storing sectors of each track. It is noted that a servo sector typically contains a pattern of data, often termed a servo burst pattern, used to maintain optimum alignment of the read/write transducers over the centerline of a track when transferring data to and from specified data sectors on the track. The servo information may also include sector and track identification codes which are used to identify the location of the transducer.
Within the disk drive system manufacturing industry, much attention is presently being focused on the use of a magnetoresistive (MR) element, also referred to as an MR stripe, as a read transducer. Although an MR read/write head assembly, typically incorporating an MR read element and a thin-film write element, would appear to provide a number of advantages over conventional thin-film heads and the like, it is known by those skilled in the art that the limited life expectancy of a typical MR read element under normal operating conditions may dissuade developers of disk drive systems from utilizing MR transducers in disk drive units designed for moderate to high reliability applications.
By way of example, historical life expectancies of MR stripes have been stated at 1,000 hours to less than 10,000 hours. The design life expectancy of a typical hard disk drive system, in stark contrast, is stated at 5 years or 43,800 hours. It can be immediately appreciated that extending the life expectancy of MR transducer elements or stripes for use in disk drive applications is imperative if reasonably long disk drive life expectancies are to be achieved.
Many disk drive systems are employed in applications in which instantaneous access to stored data is a requirement. Disk drive systems used in network servers represent one such application. In a typical server-type application, the disk drive systems may remain inactive for extended periods of time during which reading, writing, and seeking operations are not performed. Notwithstanding such extended periods of disk drive system idleness, the disk drive systems must remain in a state of readiness in order to provide for the instantaneous access to data stored thereon.
In order to provide for instantaneous access to data stored in conventional disk drive systems that employ MR transducers, the MR elements are maintained in a ready-for-use state. As such, a bias current is supplied to a selected head on a continuous basis during normal operation and periods of extended disk drive system inactivity. It has been found that deleterious electromigration occurring within an MR element is accelerated in response to the higher temperatures/currents associated with biasing the MR element for instantaneous usage during active and inactive periods.
It is understood that disk drive systems used in server-type applications, as well as in many other applications, are typically designed to provide for a long service life. It can be appreciated that maintaining a disk drive system in a continuous state of readiness during extended periods of idleness can significantly reduce the operating life of the disk drive system and, in particular, the MR elements employed in the read/write heads of the system.
There exists a keenly felt need in the disk drive system manufacturing community for an apparatus and method for extending the life expectancy of a hard disk drive system in the field. There exists a particular need for an apparatus and method for extending the service life of an MR element incorporated in a read/write head. The present invention fulfills these and other needs.
The present invention is directed to an apparatus and method for extending the service life of an MR element incorporated in a read/write head. A method of extending the service life of an MR element provided on a read/write head of a hard disk drive system according to the present invention involves detecting periods of inactivity of the disk drive system and selectively switching between the heads for purposes of reading servo information during the periods of disk drive system inactivity.
Switching between heads may involve selecting each of the heads for reading servo information during one or more periods of disk drive system inactivity or selecting each of the heads in sequence during a respective period of disk drive system inactivity. Selecting between heads may also involve selecting a head having a minimum of usage. Head usage may be determined based on, for example, operating time data or energy dissipation data associated with each of the heads.
Other head characteristics, such as head or MR element wear, may also be used to select a head with minimal usage. A head having an MR element with a minimum of cumulative operational use or cumulative energy dissipation relative to other MR elements provided in the disk drive system may be selected as the head with a minimum of usage. Selecting between heads may further include selectively activating each of the heads for reading servo information for a predetermined duration of time during one or more periods of disk drive system inactivity.
Another aspect of the present invention concerns an apparatus provided in a disk drive system for extending the service life of an MR transducer. The apparatus includes a data storage disk, a number of data transfer heads, an MR element provided on each of the heads, an actuator for providing relative movement between the heads and the disk, and a processor that selectively activates each of the heads for purposes of reading servo information during one or more periods of disk drive system inactivity. The processor may selectively activate each of the heads in sequence or, alternatively, out of sequence during one or more periods of disk drive system idleness.
A timer may be utilized to produce signals upon expiration of a pre-established duration of time, such that the processor selectively activates each of the heads for purposes of reading the servo information during system idleness in response to respective ones of the expiration signals. A memory may be coupled to the processor and used to store usage parameters associated with each of the heads. The processor may select a particular head having a minimum of operating time or energy dissipation for activation during disk drive idleness as determined using the usage parameters stored in the memory.
In accordance with another embodiment of the present invention, a method of extending the service life of an MR element provided on a read/write head of a hard disk drive system involves moving the read/write head to a target location over a surface of a data storage disk, and reducing, during a period of disk drive system idleness, the rate at which the MR element reads servo information from the disk surface so as to reduce usage of the MR element during the idle period. Reducing the rate at which the MR element reads servo information from the disk surface involves reducing the rate from a nominal number of servo samples per disk revolution associated with nominal operation to a reduced number of servo samples per disk revolution.
The rate at which the MR element reads servo information during a portion of the idle period may, for example, be reduced to one servo sample per disk revolution. The rate at which the MR element reads servo information from the disk surface may, by way of further example, be reduced by greater than approximately 98% relative to the nominal servo sampling rate.
Another embodiment of a method of extending the service life of a number of MR elements provided on a multiplicity of read/write heads involves moving the heads to a target location over a surface of a data storage disk. During a period of disk drive system inactivity, the rate at which a selected MR element reads servo information from the disk surface is reduced from a nominal servo sampling rate to a reduced servo sampling rate. The MR elements are selectively activated during idle periods so as to further reduce usage of the MR elements. The servo sampling rate of a selectively activated MR element is increased from the reduced servo sampling rate to the nominal servo sampling rate in response to a disk drive command signal.
In accordance with a further embodiment of the present invention, an apparatus is provided in a disk drive system for extending the service life of a read/write head. The apparatus includes a data storage disk, a number of data transfer heads, an MR element provided on each of the read/write heads, and an actuator that provides for relative movement between the heads and the disk. A processor controls the sampling rate of servo information derived from the disk using the MR elements. During a period of disk drive system inactivity, the processor moves the actuator to a target position, such as a position at which head-to-disk clearance is at a maximum.
The processor then activates a selected one of the MR transducers and reduces the servo sampling rate of the selected transducer from a nominal number of servo samples per disk revolution to a reduced number of servo samples per disk revolution so as to reduce usage of the MR elements during the idle period. Selected ones of the MR transducers may be activated during subsequent periods of disk drive system inactivity. The processor may initiate reduction of the servo sampling rate upon expiration of a predetermined duration of time subsequent to the start of the idle period. Reducing the servo sampling rate of a selected MR element in combination with switching between MR elements in a multiple-head disk drive system significantly reduces the cumulative time during which a particular MR element is operating.
The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.